Update One Excel Spreadsheet From Another

Here is the scenario:

I have a primary excel spreadsheet that I work from. The architecture is as follows:

Sheet 1: Called "Information"
Column A: Name
Column B: Date of Birth
Column C through Z: Various bits of information.

Sheet 2: Called "Master"
Cell B1: Contains the date and time of last update from the VBA I am asking for below.

On a weekly basis I get sent a "Update" spreadsheet that is constructed the same way as my primary. This is what I would like to do with some VBA:

From my primary sheet I run the VBA and it opens a pop up that allows me to select the updated worksheet. Next it cycles through both worksheets (Primary and Update). It compares Column A and B, if it finds a match it updates columns C through Z from the "Update". In order to get a match cell A1 and B1 of the primary worksheet has to match Cell A1 and B1 of the update sheet exactly.

The second thing I would like it to do is if the update sheet contains a new entry...in other words the update sheet has a row that does not match the primary it copies the row from the Update sheet to the Primary. In this way, the Primary sheet is always growing with new information and updating any old information it matches.

The last thing I would like to do is copy the current date and time after the comparison is complete to the Primary workbook to sheet "Master" in cell B1. This way I always know the time and date of the latest update.